This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Multiple structures that require synchrotron radiation are currently under investigation. These include 1.1 and 1.2 MDa complexes of up to 42 protein subunits (proteasome activator complexes), structures of HIV-1 Gag-derived domains that are important for viral capsid assembly and dynamics, cellular proteins and complexes that function in HIV budding, nucleosome remodeling and reorganizing complexes, and enzymes of heme biosynthesis. In many cases crystals are currently ready for data collection while in other cases crystals are likely to be obtained within the next few months/years. In some cases we need synchrotron radiation because the diffraction is inherently weak or because crystals are small. Other times we need high resolution to reliability see details of complexes that might guide future effort at drug development. Other times we need tunable radiation in order to obtain phase information or to localize anomalous scattering centers in difference maps.